You don't need to drop the transmission. I've changed dozens of seals by simply removing the pan and the rear main cap, and loosening the rest of the main bearing caps. There's enough wobble in the transmission input shaft to allow the crank to drop a little, and there are tools available to ease the upper rope seal out, and install the new one.
Lisle tool company makes a seal remover/installer kit, but a big sheet metal screw, vise grips, a piece of copper wire, and a razor blade were my seal-changing tools for a long time.
Old cork oil pan end seals can get brittle, so soaking them in hot, almost boiling water for a few minutes restores their flexibility. Use a little RTV sealer on the ends where they meet the pan side rail gaskets, but don't overdo it on the sealer.
Jerry
